CMFM: Do not use cd and pwd commands

Remove cd and pwd commands and use / as working directory for shell process (this commands
are not used). This prevents that storage volumes from get busy on unmount file systems.
Signed-off-by: jruesga <jorge@ruesga.com>

Change-Id: I772866c00233351f505b61f53d43bac5de02a5e4